Centralized traffic controlling system for railroads



1936 7 Sheets-Sh eet 1 Dec. 27, 1938. R. M. PHINNEY ET AL CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Fil ed Aug. 1

THE'ITZ ATTORNEY Die. 27, 1938.

R. M. PHINNEY' ET AL- CENTRALIZED'TRAFFIC GONTROLLING SYSTEM FOR RAILROADS 7 Shae ts-Sheet 2 Filed Aug. l, 1936 Dec. 27,

lig-l R. M. PHINNEY ET AL CENTRALIZED TRAFFIC. CONTROLLING SYSTEM FOR RAILROADS F;i.led Aug. 1', 1936 l C-J-&-H- 69" ".7 Shee'ts-Shet 3 Dec. 27, 1938. R. M. PHINNEY ET AL 2141551 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Aug. l, 1956 7 Sheets-Sheet 5 OFT Indicafions 4 u I \--l v D ec. 27, 1938. R. M. PHINNEY ET AL CENTRALIZED TRAFFIC GONTROLLING SYSTEM FOR RAILROADS Filed Aug. l, 1936 7 Sheets-Shee'b 6 R. M. PHINNEY ET AL 2,141551 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Dec. 27, 1938.

Filed Aug. l, 1936 7 Sheets-Sheet 7 INVENTORS M M 7%Zww THEH2 ATTORNEY Patented Des. 27,193s

CEN'IRALIZED' TRAFFIO CONTROILING SYSTEM FOR RAILROADS Robert M.

Phinney am! Walter H. Hoppe, Rochester, N. Y., assignors to General Ra.ilway Signal Company, Rochester, N. Y.

Application August l, 1936, Serlal N0. 93,846

7 Glaims. (01.117453) This invention relates to centrallzed traflic controlling systems for railroads and lt more particularly pertalns to mea.ns for transmittin& receiving, storing and executing controls and indications in a communication system of the multiple impulse or Coded type.

In such a system the switches and signals are distributed throughout the terrltory, with those located relatively near or adj.ak:ent to each other, together with the apparatus provided to govern these switches and sign als conveniently referred to as comprising a. field station The communication system lnterconnedts the control ofiice and the several field stations and is so organized that complete control and supervision of the various switch and signal devices at the remote locations are abtaihed by the operator in the control oce. Such a traflc sontrolling system is supplemented by the usual automatic block signal system and other local means ordlnarily provided to guard against unsafe tr ain movements, improper operation of track switches and the like.

In accordance with the present invention the communication system Comprises an eXisting telegraph, telephone or power line which extends between the control oifice and field stations upon which coded impulses are superimposed for thetransmission of controls und indications. The coded impulses are made up from ca.rrier eurrents of various frequencies and it is contemplated that sufliciently high frequencies may be used in the event that it is desired to operate the ;centralized traffic controlling system by radio by substituting antenna and ground systems for the illustrated line circuit at the oflice and ab the stations. From the following description it. will be obvious tha.t the system of the present invention may be applied to a, separate line circuit used for eentralized trafiic contro-lling operation only, although the particular advantages of the present embodiment reside in the provision of a centralized trafc controlling system operating oyer an existing line circi1it which is used for other purposes.

For convenience in describing the operatioh 01 the present invention it has been shown as applied to an existing telegraph line by means of a composite set at each location. Although the circuits are 'shown connected to a telegraph 1ine cirz'zuit anal gr ound connections, it will be understood tha.t it is also possible to operate the cantralized traific controlling system over a phantom -circuit.superimposed on two physical circuits'. lt

- will also be 'understood (hat the ca.rrier frequencies chosen for operating the centraliz ed trafllc controlling system will be such as to cause no interference with the regular currents in the lines and to be free from'interference by such currents. arate carrier' frequencies are used und referred to as frequency f, f f* f and f.

The circuits are so arranged that a.ny field station in the series may initiate the communlcatlon system into a, cycle of operations by applying a momentary impulse of frequency f followed by an impulse o-f frequency f for conditioning the various clrcuits and durlng such a. cycle indlcations are transmitted from the initla.ting fleld station to the control ofice. These indica.tions are ma.de up of combinatlons cf the presence und absence of frequency f during the step-by-step operations of the stepping relay banks provided at the control oflice and a t the various fleld stations. These combinatiqns make up codes which register the transmitting stationdn the control ofiice anti tra,nsmit indica.tions from the registered statlon in accordance w1th the trank, swltch and signal conditions at the transmittlng' statlon.

The circuits are so arranged. that the control ofiice may initiate the dperatlon of the communication system by applying an Impulse of frequency f to the line clrcuit for conditioning the various circuits. During such a, cyc1e control codes are transmitted which are eflective to se- 1ect a. desired station a.nd to transmlt controls thereto.

The system is of the duplex type, that 1s, 16 is operated through separate eycles of operation during ea.ch of whieh transmission of controls and/or transmission of indications may occur. When controls are transmitted a. station selective code is flrst applied to the line circuit for selecting the particular station with which communication is' desired and then the controls. are transmitted 110 that station. When-inclications am transmitted the particular fleld station transmitting such indications first transmits a, statlon registering ende for identifying this station in the ofiice and then the indications a.re transmitted from this station to the office.

For the transmission cf controls a. predetermined number of impulses of selected frequencies are app1 ied to the line circuit, eaxrh impulse operating step-by-step apparatus in the control oflice and at the field stations in synchronism through a, cyc1e of operations irrespective of the frequency of the impulses. 'The lengths 013 the impulse am]. time space periods are all substan- -tially equa1.

As will be explained in deta1l. five sep- For the transmission 01 indica.tions a. predetermined number o1! Impulses are applied to the line circuit for operating the step-by-step apparatus in the oce and at the transmitting station in synchronism through a. cycle cf operatlons. During such a. cycle an impulse o1 the indication carrier frequency is or is not superimposed 011 the line circit du'ring the impulse and .tlme space perlods for making up the indicatlon code comblnations.

For convenience in descrlblng the operatio'n o! this system the periods during which st'epplng impulses are superimposed on the line circuit in the control oflice will be referred to as the an periods a.nd the time spaces between these impulses will be referred to as the "ofl periods.

At the start. of a cycle 01 operatlons for the transmission of controls a, conditloning Impulse of one frequency is applied to the 1ine circuit for conditlonlng the apparatus at the ofllce and at the field stations, followed by a. number o! cf! and on" periods, the number 013 which is determined by the number 01 stepping relays, which in turn 1s determined by the size of thesystem.

At the Start cf a. Cyt:le for the trz msmission of indications, a flrst impulseof one frequ6ncy is mome'ntarily appliecl to the-line clreult for starting the system, follow d by an lmpulse of another frequency for conditioning the app9.rat us at the office a.nd at the field stations. A number of ofl" and on periods then follow, the number of whlch is determined, as above mentioned, by the slze of the system. V

Other objects and advantages of the present invention will be hereinafter set Iorth in the 'specification and claims and further details will be better understood by referring to the accompanying drawings which illustrate one method of carrying out the invention by way of example.

The drawings illustrate in a, diagrammatic manner the apparatus and clrcuits employed. For conveniemce in describing the lnvention in detail those parts having simllar i'eatures and functlons are designated in the difierent flgures by like reference characters, generally made distinctive either by the use 01 distinctlve exponents representative of their location in the system o1 by the use of precedlng numerals representative of the order o! their operation. I1: has been found convenient to illustrate contacts of certain relays on two different sheets of drawings and in this case the clrcuits which control these relays have been shown connected to full line blocks, with these seine relays indicated on an adjaeent drawing by dotted line blocks. For this reason certain referencecharacters have been repea.ted on some 0f the drawings but only where they refer 'to the same relay on another drawing.

Fig. 1 illustrates the line circuit and the arrangement whereby stepping anti control impulses are applied to the line circuit in the control ofiice by way of a composite set and whereby these stepping and control impulses are taken 01T of the line circuit a1; a field station by way of a composite set. This figure also illustrates in briei form how the indication Impulses are applied to the line circuit at a field station by way 013 the composite sei; and taken oft 01 the line circuit in the control oflice by way of the composite set. Fig. 1 includes onlythe apparatus most closely associated with the line circuit and lt will be understood that other stations are connected to the line circuit in the same manner as that illustrated in this figure. v

Figs. 1A, 1B, 10 a.nd 1D illustrate the apparatus und. clrcuit arrangement employed in the control ofllce for providing means whereby the operator may govern the switches am! signals throughout an extensive territory and whereby indications ma.y be receiv ed from various fleld stations throughout such territory. For convenience in considering the control oifice circuits, Fig. 1B should beplaced to the right of Fig. 1A, Flg. 1D should be placed to the right o! Fig. 1C und F'lg. 10 should be placed below Flg. 1A with correspondingly numbered lines in allgnment.

Figs. 2A and 2B illustrate the apparatus and circuit arrangement empioyed a1; a typical field station for providing contzol of a track switch und, associated signals and for transmitting ind1 cations to the control ofllce in accordance with the present invention. For convenience in follow- Ing the circult operation 01 the system, Fig. 2A should be placed to the right of Fig. 1B and Fig. 2B should be placed below Fig. 2A with correspondlngly numbered lines in alignment.

The symbols und are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of dlrect current und the circuits with which these symbols are used a.lways have current flowlng in the Same direction. tha.t is from to The symbols (B+) und (B) are employed to indicate the positive anti negative terminals respectively 013 a. suitable battery or other source of direct current having an intermediate tap (CN) and the circuits with which these. Symbols are used may have current flowing in one directiou er the other depending upon whether the terminal (3+) or (B) is used in combination with tap (CN).

Plate batteries have been illustrated in connection with the various vacuum tubes used in the present system and although these batteries have been separately indicated, lt will be understood that a single source of platze current may ordinapily be used at a. single loca.tion for supplying all 01 the tubes. Although the filament energiz- Ing circuits for the various vacuum tubes have not been illustrated, it will be obvious that these circuits ma.y be energized from any desired source of supply, such as a battery, alternating current or rectifled alternating current. It will also be understood that rectified alternating current may be used in place of the plate batteries illustrated. Furthermore, no grid potential sources are illustrated but lt is wel1 within the scope of the present lnvention to apply such bias potentials when needed.

Control 0fiice equipment.-The control oiflce (Figs. 1A, 1B, 10 and 1D) includes a control machine having a group of control levers for each field station, a. miniature track layout c0rresponding to the track layout in the field and various indicating lamps or equivalent devices, together with apparatus and circuits to accomplish the desired operation of the system.

That part of the control oflice illustrated shows more particularly the portion o1 the control machine which is typical of the apparatus for select- Ing any one of a plurality of fleld stations, for transmitting controls to a selected Station, for registering the identity of transmitting field station in the oflce and for receiving indications from a, transmitting station.

The illustrated apparatus includes a starting button SB associated with a particular station, whieh button controls the operation of a storing relay SR und. a code determining relay CD, both ssociated with the station corresponding to button ISB. It will be landerstood that there will be a starting button ancl associated SR and CD relays for each station in the system which ls to be selected frbm the control ofllce. 'Iypical apparatus for controlling the operatlon 01 trafllc signals has been illustrated und comprises signal lever SGL. It will be understoocl that other signal levers may be provided and that levers for cantrolling the track switches ma.y likewise be provided, but for convenience onlylever SGL is illustrated since the control of one or more track switches and other signal's may be understood by analogy to the control by lever SGL, which will be explained in detail.

Code jumpers are selected by the circuits cantrolled by the CD relays, only one of which has been illustrated and which is for the purpose 01 applying a station selecting code to the line circuit in response to the initiation of the system when the associated starting button is actuated. One ende Jumper indicates that the desired Station is selected an a Single step ofthe cycle and when the num ber of stations is larger, then of course additional code jumpers will be provided and selected on additional steps of the cycl Code sending relays IF and 2B are 1or the purpose of applying the proper frequency to the line circuii: during the transmission of controls. With telay lF picked up, frequency f ls applied to the line circuit with relay 2F picked 'up, frequency f is applied to the line circuit and with both relays lF and 2F' picked up, both frequencies f and f are slmultaneously applied to the line circuit.

Relays F, FA and FB are the Impulse repeating relays operated in various combinations (as will be fully described) in response to the impulses of either or both frequencies applied to the line circuit. Slow acting relay SA is for the p n se cf defining the bounds of an operating cycle, that is it is pickeciup ai: the beginning of each cycle, is held up throughout the cycle and is dro pped oub during the "clearing out period a1: the end of the cycle. Relays SB and SC repeat the SA relay operations ancl are likewise maintained in their picked up positions throughoui: each cYcle.

Relay C is a control cycle controlling, relay, being piclced up ai; the starb of a control cycle and dropped out at the end of such a cycle. Relay CF is an indication cycle controlling relay, being picked up in response to a, field start at the beginni ng of a cycle and dropped out ab the end of such a cycle. During a duplex cycle, relays C and CF may both be picked up. Impulse coutrolling relay E is for the purpose of timing the off" and on periods during a cycle o1 operations in response i;o the operation cf the stepping relays which respond to these off" and "on" periods.

Associated with the line and line repeating relays is a bank of stepping relays inclucling relays IV, 2V, 3V, together with half-slzep relay VP. 'Ihis Dank of stepping relays is for the purpose of markingpfi i;he successive steps cf each cycle, Ehe stepping relays being successively picked up during the ofi periods and relay VP being shifted in position during each on" period. Relay 00 is a cycle controlling relay, being picked up ab the start of a cycle 0f any dass and maiutained picked up until the end of such cycle. Relay LS is included in the stick clrcuit of any CD relay which is picked up anal is primarily for the purpose of opening the chain circuit leading to other SR. relay contacts, so that oniy one CD relay can be picked up ab any one tixne.

Three frequiancy generators are lllustrated in Fig. 1'A which generate trequencies f, f, f. und

frequeney generators are applied to the line circuit through transformers and condensers of such characteristics that. the required trequency will be passed through these respective circults with minimum attenuation, while frequencies above andbelow those required to be transmitted will be sharply cut ofl.

Ale'vel contml unit 4LC is illustrated in Fig. 1C through which frequency f als transmitted by way 01 transformers 4TFR and 4TFRI 1:0 amplifier 4AI. Currents of this frequency appearing in the outpui; of amplifier 4Al are applied the input of amplifier 4A2 by means of transformer 4TFR2 and the amplified currents in the output 015 amplifier 4A2 are rectified by rectifler 4RC and appliedto the windings cf message receiving relay s MB ancl M1". It will be n'oted thal: amplifiers 4Al and 6A2 are of a diiferent type from the amplifiers ai: the field station for amplifying frequencies J, f, f-". Ihe reason f or thls is that higher gaixi amplifiers are proposed for amplifying the indication frequencies, because in is assumed that these frequencies appliedat the field stations will be of considerably lower level than the frequencies applied in the cor;trol office.

Pilot relays IPT and 2PT are of the polar magnetic stick type and are positioned in accordancewith a Station identifying code received in the control ofiice during a duplex cycle or a cycle during wh.ichindications alone are transmitted. Station relay ST is assumed to be associated with the station illustrated in Figs. 2A ancl 2B, lt being picked up in response to the station identlfying code transmitted by this station. It will be 4 understood that obere ls a separate ST relay for each station to be registered in the control offlce, these relays being selected by the diiferem; positions of the pilot relay contacts. Indication receiving relays IIR am]. 2IR. are also cf the polar magnetic stick type and are positioned. in accordarice wii;h the indications received from a transmitting station during a cycle in wh.ich indications are transmitted.

Field station equipment.-The field station illustrated in Figs. 2A and 2B is typical of all stations of the system and may b'e adapted for use at i;he first, second or any other location by merely ltering certain Code jumpers to provide for the desired codes. For convenience in the de-' scriptions, this field station has been specificaliy illustratedas being the first of the series by reason 02 the distinctive exponents employed and lt; will be underslzood that other stations may be connected to the line circuil; between the illustratedl station and the control otlice o1 ai: points more distant from the control ofice than the illustrated station.

A track section is illustrated, With track switch TS which is eperated fi 0n1 one extreme lockeol position to the other by means of switch machine S1VP. illustrated tracl: section for governing trafiic thereover and these signals, as wellas the switch machine, are governed from the control oflice through the medium of the communication system. Signal relay SGR is shown to illustrate how east and West signals are seiectively Controlled and relay SS is illustratecl 120 show how these signals may be put to stop, all in response Suitable signals -are associated with the Y toachoice of threecodes transmlttedatasingle step of the cYcle. The control of the switch machine by a switch machlne relay in response to controls has been omitted, since such control ma.y be clearly understood by analogy to the control o1 the slgnal relays whlch will be descrlbed in deta.ll.

The communicatlon part of the system includes line relays IF and 2F, whlch respot'xd to frequencies f and f respectively, these frequencles being received in the output of amplifier A und applied through level control unlts ILC and 2110 by way of transformers IT! and 2TF 'to the input circults of ampllfiers IA a.nd 2A throughtransformers ITF und 2TF. The amplified carrier frequencies in the output circult.s o1 these amplifiers are supplled to relays III. a.nd 2F by way cf transfdrmers I'IF' und 2TF and rectifiers IRC and 2RC. A band pass filter is ilhistrated in Fig. 2A which is deslgned 120 pass frequencies f, f, f a.nd f, with these frequencles being applied to the Input of amplifier A by way of transformer TF For the purpose cf illustrating the selection of a statlon for the transmission cf controls, re-

lays SO a.nd SOS a.re shown and II; will be exp!alned in detail how these relays are picked up at all stations at the beglnning of a cycle und selectively dronmd out until only the one to which controls a.re to be transmitted remains picked upthroughout the cycle cf operations. Relay FB repeats the operations of the I1 and 2F relays and controls the operation of the associated steppingrelay bank in a, manner which has not been lllustrated in detail, but whlch is the same as the control of the stepping relay ba.nk in the control ofilce by relay FB. 'I'his coutrol is merely indlcated by dotted llne connection ISO. Relays SA am]. SB, cf the s1ow-act- Ing type, operate in a manner simllar 1:0 and are for a purpose similar to correspondlng relays in the control ofice.

A field changc rela.y CH Is illustrated In Fig. 2B I;o show how a cycle of operations is initlated from a field station. For the purpose of illustrating the manner of determiningwhen a. fleld station is I:o transmit its indlcations, relays SI and SIS are employed. As will be explained in detail, these relays provide the superiorlty of code type cf lock-out so that only one field station can transmit its indications during a, cycle when severa.l field stations have Indicatlons ready to transmit a.t substantially the sa.me tlme.

Rela.ys PB and PF' are for the purpose cf superimposing the indlcation carrier current on the line clrcult during the o und an periods cf a cycle for making up the lndication codes. For the purpose of indicating how indlcations are transmitted from a station after such station ldentifies itself in the control office, track relay -T und signal lndicating relay M are Illustrated. Although the control circuits for these relays are not shown it will be und:rstood that relay T in its plcked up position, indlcates that the associated track sectlon is unoccupied und when this section becomes 0ccupied relay T is dropped Furtherm ore it is assumed that relay M, when in Its picked up posltion, Indicates that all signals associated with the illustrated track sectlon are at stop und when Imy one of these signals is clear relay M is dropped.

Carrier frequencles f and f reoeived in the output of amplifier A are applied to the Input circults of amplifiers 3A and 4A by way of transformers 3'I'F and 4'IFZ and by way cf level control networks 3LC and 4LC respectively. These carrler frequencies are amplified by amplifiers 3A and 4A with frequency f belng rectifled by rectlfier 4RC for operatlng message relay ME Relay ME 1s for the purpose of cooperating wlth lndlcation code transmitting relays F'B am]. PF for ruling Inferlor staticns oft the line," by dropping out thelr associated SI relays and Ior maintaining the SI relay energized ab a. superlor station, In response to a. statlon identlfying code beingtransmitted over the line clrcuit to the oflice.

The level control units lllustrated In the coutrol oflce und at the field station are 1'or the purpose cf malntaining the s1gnal level applied to the amplifier, to whlch each level control unit is connected, aI; the des ired value for the varlous frequencies, which value might otherwise be 1mprope: due to line attenuation.

An oscillator mixer tube OSM is illustrated in Fig. 2B for the purpose of'mixlng cscillating frequency f with the received monitorlng or synchronizing frequency f for providlng indlca-' tion frequency f, which preferably has a definite frequency relation 1:0 the monitory frequency f a.nd hasthe same frequencyas similar frequencies f generated at other field stations. In other words the oscillating circuits assoclatedwith vacuum taube OSM preferably provlde an oscillating frequency f whlch is dominated by synchronizing frequency 1 1:0 provide a resultant indication, transmitting frequency j. The purpose of such an arrangement will be explained in detail later in the specification. The indlcation carrier frequency currents are applied to the line circuit by way of transformer 4'I'F'I.

II; is believed that the nature of the Invention, its advantages am). characteristic features will best be understood with further description being sei: forth from the standpoint cf operation.

Operation Manual start.-For the purpose of explaim'ng the operation of the present system lt will be assumed that lever SGL is actuated to its right band (West) position for clearing a. signal for governing west bound traffic at the station illustrated In Fig. 2A. Starting button I SB is actuated to start the system into operation and this closes an obvious pick-up circuit for starting relay SR. Relay SR, closes a, stick circuit foritself extending from back contact III of relay CD, front contact II and winding of re1ay SR to A circuit is now closed for picking up relay CD which extends from back contacts I2, I3, I4 and I5 of relays SA, LS, MF and MB respectively, front contact I6 of relay SR and lower winding of relay CD to Relay CD closes a stick circuit for itself which extends from back contacts 60 and 62 in multiple of relays E and 3V respectively, conductor III], winding of relay LS, freut contact 63 and upper winding of relay CD to Since the winding of relay LS is included in this stick circuit, relay LS picks up and opens back contact I3 for preventing the picking up of any other CD relay, in the event that another oflice starb is stored by the picking up of another SR relay in response to the actua.tion of another SB button. The opening of back contact I0 of relay CD deenergizes relay SR.

A circuit is now closed for pickiug up relay C Fig. 1B which extends from front contact I7'of relay LS, conductor III, back contact I8 of relay SC and winding cf relay C to The picking up of relay LS also opens the clrcult extendlng 120 the upper windlng cf relay 2F a.t back closure offront contact 23 cf relay C starts the three frequency generators into operatlon for generatlng frequencies f j and Frequency 1 is lmmediately applied to the line circuit by way of ttansformer 3 TF and the multiple circu1t leading to the composite sei; connected to the Brie circuit in the control oflice including comduct0rs ll2 am! H3. It will be pointed out at this t1me that the condensers in the prlmary und secondary windings cf transformers R'IF, 2TF, and 3'I'F are cf the propervalue to sharply tune these circuits to the frequencies which they are to pass.

Relay OC is now picked up over a circuit extending from front contaci: 22 cf re1ay C, back contact 23 01 relay SB and winding cf relay OC to Relay 1F is picked upcver a circuit extending from back contact 25 cf relay E, front contact 25 of relay OC, front cantact 26 of re1ayfC. back contacts 27, 28 and 29 cf relays 3V, 2V and IV respectively, conductor H, and upper winding cf relay IF to Relay IF completes the circuit from generated frequency f to the primary df transforme: fl'IF loy way of front contact 30, so thatfrequency f is applied to the line circuit by wa.y of the secondary cf this transformer.

The above explanation relates to the initiatic1r1 of the system from the control ofiice and H: will now be explained how the circuits are conditioned in thecontrol oce and ai: the field stations fcr receiving the ende which is appliecl to the Eine c1rcuit. 'Ihe picking up of re1ay GF closes an V obvious circuit at its front contaci; fl for picking up relay F and relay F closes an obvious circuit ab ibs front contact 32 forpicking up relay SA. Relay SA closes an obvious circuit a1; 1ts front contact 33 for picking up relay SB by way et conductor l I5 and relay SB closes an obvious circ1.t at its freut contact 35 for picking up relay SC. Relay SA closes a circuit for picking up relay FB which extends from front contact 35 cf re1ay SA, back contact 3E cf relay FA and winding of relay FB to Because of the slow-acting characterlstics cf relay SA, this re1ay will be maintained; in its picked up positlon throughout the operaing cycle unt-il the clearing out period a1: the end cf the cycle ancl its repeating relays SB and. SO

will likewise remaln picked up until the clearlng out period. Relay SA maintains relay C energized during the cyc1e by means cf a stick circulb extending from front contaci: 92 cf relax; SA, conductor l2, freut contact S and winding cf relay C to Frequency f applied to the line circuit 15 received through the composite sei: at the. fielc1 station illustrated in Fig. 2A (and ab all other field stationshis transmitted thrcugh the band. pass fi1ter illustrated in Fig 2A and applied 120 the input of amplifier A by way cf transformer TF Frequency f appears in the oubput cf amplifier A and is applied to the input 015 amplifler !A by way of transformers ITF E'IF anti ievel control network ILCK This frequency is again amplified by amplifier 1A and appears in the output circuit of this tube, where it 1s repeated by transformer l'I'F'-* and rectified by rectifler IRC for operatlng relay F It will be umlerstood that, by means cf similar circuits a1; the other stations, the IF relays at thcse other stations will also be plcked up.

Relay. IF closes a clrcuit for plcking up relay FB which extends from freut contact i5l cf relay IP, back contact 152 cf relay SB a'nd winding of relayFB to Relays SO and S08 are picked up over a c ircuit extending from back contact 153 of relay SB, front contact 056 of relay IF back contact l55 of relay 215, back contacts I56, I51 and l58 cf relays 3V 2V and IV respectively and 1ower windings cf rclays SO am]. SOS in series to Relay SA is picked up over a circuit extending from front contact H5! cf relay IP, back contact 159 cf re1ay SO and winding cf relay SA to A substitute circuit for intermlttently energiz'mg relay SA durlng the following cycle is closed at front contact 1613 cf relay FB Relay SA closes an obvious pickup ci1cuit for relay S13 at fron'c contact IM.

A stick circuit is closed for relay 80 extending from iront contact I53 cf re1ay SBR front contacts H52 and H53 of relays SOS and.

' SO respectively and upper winding of re lay SO- contact 065 and upper winding of relayS0S tc It will be understood that the FB SA, SB, SO and SOS relays at all other stations are picked up during this conditioning period and will he later explained how the SO and SOS re1ays are dropped out ab non-selected st'ations.

Impulsing und stepping operations.-It will first be assumed (and later explained) that; the 6F and 2F Code sending relays are positioned in accordance with the control code t0 be applied to the line circuit, for energizing the 1ine circuit with frequency f, frequency 1 or both cf thesc frequcncies simultaneously. For the presentit will be assumed that relay IF (which was pickc up as previously described to apply frequency j to the line circuit) is dropped to removc this frequency from the 1ine to mark the end cf Ehe couditioning on period. It will be assumed that relay !F is picked up to apply -frequency to the line circuit for the first coded impulse and dropped.to mark the end of this impulse or on" period. Ic will be assumed that both relays EF and 2F are picked up to apply frequencies f and j? 130 the line circuit during the second "on period and tha.t these relays are dropped to mark the en cf this "on period. It will then be as sumed that relay 2F is picked.up to applyfrequency 1 130 the 1ine circuit for the thirdon period and that this relay is dropped to mark the end. cf this on period and the beginning of the clearing out period. 115 will be 1ater explained how relays IF and 2F are selectively energized in accordance with the code t0 be transmitted.

The picking up of relay SB (above described) closes a pick-up circuit for relay VP which extends from freut contact 37 of relay SB, conductor Il, front contact 38 of relay FB, couductor HIT, back conact 39 0f relay IV and winding cf relay VP to Re1ay VP closes a first stick circuit for itself at its front ccntact M which is independent cf front contact 38 cf relay FB. Relay E is now picked up over a circuit extending from back 'contactsrfl, 52 and Q3 of relays 3V, 2V and V resp&ctively, freut;

contact 44 of relay VP, windlng of relay E and front contact 46 of relay SC to The picking up of relay E opens the above describ8d plck-up clrcuit for relay IF at back contact 24 and relay I F drops to remove frequency f frnn the ]1ne 130 mark the end cf the condltionlng an period and the beginning of the flrst otf" period.

The dropping of relay IF opens the energlzing circuit cf relay F at fr ont contact 3l relay F drops and closes a pick-up clrcuit for relay FA which extends from front contact 35 cf relay SA, back contact 46 cf relay F and wlnding of relay FA to Relay FA opens the above descrlbed circuit for relay .F'B a1: back contact 36 and relay FB ls dropped. A second stick circuit is now closed for relay VP which extends trom freut contact 31 cf relay SB, back contact 38 of relay FB, front contact 47 and wlnding cf relay VP to Relay IVJs now p1cked up over a circuit extending from back contact 48 o1 relay FB.

conductor I I8, front contact 49 of relay SB, frcnt contact 58 of relay VP, back contac't 5I of relay 2V and windlng cf relay IV to Relay IV closes a stick clrcult for ltse11 extending from front contact 31 cf relay SB, freut; contact 62 and winding cf relay IV to It will be mentloned ab th1s point that slmilar stick circuits are closed by relays 2V and 3V at thelr freut contacts 53 and 54 when they are plcked up later in the cycle. The picklng up cf relay IV opens the above described energizing circult for relay E at back contact 43, relay E drops and closes a pick-up circult for relay IF (later described) and the plcking up of relay IF applies frequency f t o the l1ne tc mark the end cf the flrst ofi" period and the beginning cf the first on period.

Relay F 1s now picked up over the prevlously described circult including front contact 3l cf relay IF and relay FA is dropped because cf open back contact 46. The dropping cf relay FA again closes the pick-up circuit for relay .FB at back contact 36. The picking up of relay FB effects the dropping of relay VP because its first stick circult is open at back contact 38 cf relay IV and1ts second stick circuit is open at back contact 38 cf relay FB. Relay E is now plcked up over the previously described clrcult but whlch now extends through front contact 43 ofrelay Wand back ccntact. 44 cf relay VP and relay IF is dropped because of open back contact 24 cf relay E. The droppin'g cf relay lF'removes frequency f from the line to mark the and o1 the first on" period and the beginning o1 the second off" period. v

Relay F is now dropped because of open front contact; 3I relay FA 1s picked up because cf closed back contact 46 and relay F13 is droppe because cf open back contact 36. Relay 2V1s now picked up over a circuit extending from back coutact 48 of relay FB, ccnductor H8, front contact 49 cf relay SB, back contact 58 of 1 elay VP, back contact 55 of relay 3V, front contact 56 of relay IV and winding of relay 2V to Relay E is now dropped because cf open back contact 42 cf relay 2V and relays IF and 2F are picked up over circuits later to be described. The picking up of relays IF and 2F applles frequencies f and f to the line circuit which marks the end cf the second oft period and the beginning cf the second on period.

Relay 1- is now picked up because cf closed front contact 3l and lt will be understood that in the event that only relay 2F1s picked up, relay F would b e energized because of front contact 57.

Relay FA is dropped because of open back contact 46 and relay FB ls plcked up because cf closed back contact 36. A clrcult is now closed for picking up relay VP whlch extends frqm front contact 31 of relay SB, conductor H6, front contact 38 cf relay FB, conductor ll'l, back contact 58 of relay 3V, front; contact 59 cf relay 2V and winding of relay VP to Relay VP again closes its first stlizk circ'uit at front contact 48, which includes the above described circuit independent cf front contact 38 of relay FB. The picking up of relay VP picks up relay E because of closed front contacts 42 and 44 01 relays 2V and VP respectively. The picklng up of relay E drops relays IF and 2F because cf open back contact 24 and the dropping cf relays IF and 2F rexnoves frequencies f and from the line to mark the end cf the second on'! period and the beglnning cf the third 01T period.

Relay F ls now dropped because of open front contacts 311 and 51, relay FA is picked up because cf closed back contact 46 andrelay FB 1s dropped because cf open back contact 36. The second stick circuit for relay V'P 1s again closed as prevlously descrlbed and relay 8V is picked up over a clrcuit extendlng from back contact 48' cf relay FB, conductor H8, freut contact 43 o1 relay SB, freut contact 56 cf relay VP, Iront contact 5I of relay 2V and winding o1 relay 3V to Relay Eis dropped because o1 open back contact 4I and relay IF, or 2F or both will be picked up (as later descrlbed) mark the and 01 the third ofi period and the beginnlnz of tba *hird an period.

'Ihepicklng up of relay IF, or relay 2F, closes the obvious pick-up clrcuit for relay F, relay F drops relay FA because cf open back contac t 46 and relay FB 1s picked up because of closed back contact 36. Relay VP ls now dropped because its first stick circuit is open at back contact 58 cf relay 3V and its second stick circuit ls open at back contact 38 of relay FB. Relay E ls now picked up over the above deacrlbed clrcult, but now includes front contact 44 0f relay 3V and back ccntact 44 of relay VP. The plcking up o! relay E drops relay IF, or 2F or both because 01 open back contact 24 to mark the end o1 the third an period and the beginnlng of the "clearing ou period.

Relay F is now dropped because 01 open front contacts 3l and 51, relay FA'is plcked up because cf closed back contact 46and relay FB 1s dropped because of open back contact' 36. Since there are no other stepplng relays to be picked up, the condltion of the E relay (plcked up) is not changed and relays IF, 2F and Fremain down for a sufflclently long interval. of time to drop relay SA because cf open frontcontact 32 01 relay F. Relay FA is now dropped because cf openfront cont act 35 of relay SA and relay SB is dropped because of open freut contact 83 of relay SA. Relay C is dropped because of open front contact I2 cf relay SA and relay C stops the operation of the frequency generators because of open front contact 2l. Relay SO is dropped because of open freut contact 34 cf relay SB and the stepping relays are dropped because thelr stick circuits are de-energized at open front coutact 31 cf relay SB. The dropping cf the stepping relays anc i the d ropping of relay SO drops relay E because of open front contacts 4l and 45 cf re1ays 3V and SO respectively.

During the operation cf the cycle jusbdelay E by means of a stick circuit extending through freut contact 66 of relay E. front coutact M of'relay OC, front contact 23 of relay SB ami winding of relay 00 1:0 At the end of the third an periocl, relays LS and CD are dropped when relay 3V picks up and opens its back contact 62. When relay SA drops and closes its back contact I2, any CD relay in the bank can be picked up in the event tha.t a. stored statt has been efiectted by operating the associated starting button. When relay SC drops, a field start can be received in the ofiice because of closed back contact 85 of relay SO a.nd at this Same time an ofiflce staut can be efiective 120 picl: up relay C because of closed back conte.ct I8 cf relay SC. 'I'his condition, which permits the pickingup of relays C and CF ab the start of a.

cycle, will be more clearly understood in connection with the description of a duplex cycle cf operations.

From the above despription it will be apparent tha.i: frequency is applied 110 the 1ine circuit during the initlat-ing period, remains on the line circuii; throu'ghout the cycle and is removed when relay C drops to stop the operation of the frequency generat0rs. This applicatlon of frequency to the line circuit is 01 no eifect during a. cant101 cycle and its purpose will be explained in connection with an indication cycle. Relay F13 at the illustrated fleld station is dropped ab the beginning of the-"clearing out period to efiect the dropping cf relay SA because cf open freut contact BSE ancl relay SB is dropped because of open front contact fii. 'Ihe particular SO relay at the selected field station will be dropped out during the clea1ing out perlod when relay SB drops and opens its fron t contact 153.

As prevlously mentioned, the stepping relays ab the station illustrated in Fig. 2A will operate in synchronism With the stepping relays in the ofllce by circuits not shown but which are indicated by dotted line 55%. Ai: those stations which are dropped 011t- =iuring the station selection portion cf the control. cycle, the FB relays are not Qperated because @i open freut contact E59 cf ehe SO reiays. S'ince the FB relays du not operate at these dmppe=ri -auia stations the associated step-' ping r'e1azrs ape=rating a1; such stations.

Althov.gh station may be dropped out for control selection during a cycle, this station may comtinue to step in the event o'hat indications are being transmlttecl during this cycle and in this eveni; the FB rela5rs Will be intermittently operated m operate the associated stepping relays because cf the closed f1ont contact l6 of relay SI Front contacts l''l and E63 of re1ays 81 and S0 lea.cling to dotted line fl, indicate tha.t stepping is dependent upon a. station being selected by its SO relay beim; pickecl up 0r by its SI relay being pickecl up. 'Ihe stepping relays which axe picked up durlng falle cycle are droppecl ou1; during the clearing eub period at the end of the cycle in the same manner explainecl in connection with those in the control office.

Selection of c mrlrol code.-Jumper 9 (see Fig. 1A) connected in its full iine posiclon as illustrateci determines thac the first on period. (first coded impulse) is tobe frequency f 'I'his is effectecl by picking up relay lF a1; the end of the firsi; ofi period over a circuit extending from back contact 2% of relay E, front contact 25 0f relay OC, freut contact 26 0f relay C, back contacts 27 "and 23 0: relays SV and 2V respectivelY, front contacb 29 of rela.y W, conductor H9, front contact 8 of relay CD, Jumper 9, IF bus and upp'er winding of relsy IP to Withreiay flI picked up, frequency 1 is appiied to the line circuit during i:he ilrsb on" period becase of closed front contact 353.

In the event tha.t Jumper Q is in iiss centex dottted line position, then the above described circuit extends by way of the 2F bus and the upper winding of relay 2F to This eflects the picking up of reiay 2F and frequency j is applied to the line circuit because 02 closed freut contact 68. In the event that Jumper 9 is in ita right band dotted position then the above described plck-up circuit extends through the lower windings of relays lF'and 2F in series to This eifects ehe picking up f both of these relays to simultaneously apply frequencies 1 and I to the line circuii: because cf closecl front cantacts 3fl and 66.

This choice of three c0des applied the iine circuit during the first 011" period is' illustrateci to indicate how station selection is accomplished on a single step cf the system. It will be oluvious thai;, in systems of larger capacity, additional code jumpers Will be provideci und selecte ci on one er more additional steps of the stepping periool is debermined by the position of lever SQL. With this iever in its right band position as assumed, frequency 1 is appiied to the lin e because the ende seiecting circuit extending through front contact 28 of relay 2V.conductor i2ll, and freut conta.ct 1 of relay CD, picks up rela.y 2F by Way of lever SGL in its righij hand dotted position. In the event that iever SQL is inits left band. dotted position, then the second code will be frequency f because relay IF will be picked up over the above described circuit and now. including lever SGL in its left band dottecl posltion. In the event that lever SGL is in its mid (stop) position, then the above described selecting clrcuit includes both windings cf relays 'EF and 2F so that both frequncies f and f are applled o0 the line circuit.

Although the circuit extending through freut coritact 2T! of relay 3V is not shown completecl, it will be understood that this circuit; ma.y be comnected to an additional leve'r such as a. switch machine control lever, im: determining the frequency cf the third impulse.

Station selectzon for controls.For convenience in describing the opera;tion cf station selection, reference will be made to Fig. 2A which illustrates a. typical fleld station somewhat in detail anal whichis considered to be tl1e firsi: station of the series and. selected by station selecting ende f applied to the line circuit duringthe flrst an period, as previou sly explained. The illustrated field station is rendere responsive to this particular ende because of the connection of jumper E9@ in its fuli line position. It will be understooc'i that a jumper similar 1% at the station responding to codie f during the first on" period, is connected in. its center dotted line position and that a station responsive to code f, f during the first an period has its code jumper connected in its lower dotted iine position. It will also be understood that the FB relay will be impulsed in resporise to the operation of relay 2F ab selected stations because of froni; contaci: i'll which energizes the same circuit as contact 151 of relay IF I1; was previovxsiyexpiained chat reia.ys S0 und S05 were picked up during the condition- Ing "on period and their stlck circults were pointed out. When relay FB is dropped at the beginning of the first off" period by the dropplng of relay IF relay 80 is stuck up over a circuit extending from front contact l53 of relay SB back contact Ili4 of relay F'Bl, front contact I63 and upper wlnding of relay S to During the flrst "o period the circuit including the lower windings of relays SO and 308 ls de-energized at open front contacts IC and l55 because both relays IF and 2F .are down. Relays SOS is dropped durlng the flrst ofl."' period because its stick circuit ls open at front contact l64 o1 relay l"B.

When relay I1 is picked up 'at the'begixming of the first on perlod in response to code frequency f the selection is made for picking up relay SOS and maintalning relay SO plckecl up. This selection is made over the circuit extending from front contact I'll! of relay S0 freut contact I54 oi relay IF back coutact I55 of relay 2F, back contacts l56 am! 151 of relays 3V and 2V respectlvely, freut contact l58 o1 relay IV jumper I99 in its full 1lne position and lower windings .of relays S0 and SOS to 'Ihis selective circuit ls completed by relay IF before relay FB picks up to open the above descrlbed stick circuit for relay SO at back contact I64. Rhlay SO ls therefore prevented from dropping out and relay SOS is plcked up, so that the above descrlbed stick circuit for relay S0 is completed by way of front contacts l62 and I63 and the above described stlck circuit for relay SOS is completed at front contacts l64 and l65.

By means of this selectlve circuit the energization of relay 80 is made dependent upon the flrst code element applied to the llne circuit as repeated by re1ay IF closing its front contact IN. In the event that this code element comprises frequency f", then the above described selecting circuit extends through freut contact I55 of relay 2F, back contact I54 of relay IF, back contacts l'l2 and I 13 of relays SV and 2V respectively, front contact I'll of relay IV to the center polnt of jumper connection l99. This would eflect the dropping out cf relay S0 because cf the open jumper connection at thls point, but in this case the SO relay at the station having its code jumper in the center position would be mainta'lned energized.

When relay FB is dropped in respons'e to the dropping of relay IF at the beginn.lng of the scond "ofi perlod, relay SOS is dropped because cf open freut contact l64. Relay S0 is stuck up at this time because cf the previously described stick circuit by way cf its front coutact I63 which is completed at back contact l64 before lt is opened at front contact l62. The picking up of relay 2V during the second fofi period establishes a permanent stick-circuit (permanent during the rest of the cycle) for relay SO, which circuit extends from freut coutact l53 of relay SB ,-.front contact I'l5of. relay 2V front contact lli3 and upper winding of relay 80 to From the above lt will be apparent that a code jumper slmilar to I99 01 Fig. 2A is provided at other field stations, but connected in difl'erent posltions ior making these field stations selectlvely resp'onsive to different codes applied to the line circuit. With the provlsion 01 a slngle code jumper 9 in the ofilce and its associated code jumper 199 at the illustrated fie1d station (and slr'nllar 'jumpers at other statlons), three different code combinatlons are possible during the single Impulse per-lud whlch is used tor station selectlon. Two of these may be employed Ior statlon selection with the third belng used for the control phantom code. This is because the system will lnherently transmit a series 01 j impulses during the station selectlng step ot the cycle lt no CD relay is plcked up because o'f closed back cont act I9 o1 relay L8, due to the system belng ln itlated from a field statlon. It will be understood that when two steps are used tor station selectlon tor controls, either combinations may be used ior selectlng.statlons with the ninth corresponding to the control phantom code.

Transmission of controls.-It will be recalled that the code comblnation applled to the llne circuit durlng the second an period consisted cf frequency f as determined by signal lever SGL being in lts right band dotted posltion and thi.s code is re'ceived at the selected fleld statlon by the plcklng up of relay 2F A circuit is clo. sed for actuating the polar contact of signal relay SGR' to the rlght which extends from tront contact I'll! o! rel9.y SO, freut contact l55 01 relay 2 F back contact l54 of relay II, back contact l'l2 of relay IV, front contact I'll -oi.' relay '2V lower winding o1! relay SGR and upper windlng ot rel ay 88 to The polar contact o; relay 88 is likewise positioned to the right and a circuit is completed (not' shown) tor clearing signal WS.

In the event that lever SGL ls in its lei't hand v dotted (east) position for applying trequency 1 to the line during the second on" period, then relay IF ls plcked up and a circuit is completed for actuating the polar coutact cf relay SGR. to the left and the polar contact of relay Stil to the right for completing a signal clearing circuit ior slgnal E8 Thls circuit extends from front contact ll0 o! relay S0 freut con- In the event zum; lever SGL 18 in its center" (stop) positlon for applylng both frequencies f and f to the line circuit durlng the second on" period, then relays IF and 2F will bpth be picked up so that neither o1 the above described circuits 1or relay SC1R will be completed, but a circuit will be completed for the lower windlng o! relay SS which extends from freut contacts I'M, l'l8 and i'll o! relays SO, 2F and IF respectlv'ely, back contact l'l8 o! relay 3V, front' contact I 19 01 relay 2Vl andlower wlndlng o! relay SS to The energization 01 the lower winding of relay SS positions lts polar contact to the leit so that both signals are put to stop.

In a similar manner additional steps may be used for transmitting additional controls to the selected station for controlling the switch machine, by energlzing a swltch machine control l'elay in accordance wlth the frequency of the impulses applied to the line circuit as determined by the position of a. switch machine control lever. However, since the above typical examples illustrate the manner of such transmission lt ls believed unnecessary to point out in detall how this control is efiected.

2141551 Brin: the o'peration oi a. control cycle no iihpulses 01 i'requency I are superimpos'ed an the -llne circuit a.t a. fleld station, because n is. as-

sumed that no SI relay is picked up ior eiifecting the operation o! the f trequency generator at any station. 'Ihis results in neither reia.y MB nur M1" (see Fig. 1C) being picked up during a. controi cycle und thereiore (B) is appiied through the back contacts of these relays during the indication station registration step o! the cycle i'or positioning pilot relays' IPT und 2P'I 1:0 the left. Such a code must noi: registerany field station in the control oflice und theretore the contacts o! these two piloi; relays in their lett band pogitions in combination do not select any station relay.

The selection a.nd operation ofa statten reiay for identifying a. calling fleld station in the oflice will be descrlbed in connection with the transmission Qf indications. Aseries o! "oi! und on" periods of a cycle. during which no l carrier current is received in the control ofllce during the station seiectiug steps o! the cycle results in an indication phantom ende.

Transmission o) indications. Alth h th system is 01' the duplex type and indications may be transmitted from any station to the control ofllce during the Same cycle thai; controls are transmitted to the same o1 some other station. lt is convenient to flrst explain the transmission of indications alone ona separate operating cycle before considering the duplex feature of the system.

The manner in which fleld stations are allowed to transmit'only one a1; a time in a. predetermined order will be explained in connection with the superiority of ende lock-out ieature, this leature being included in the description following the description relatlng to the transmission. of indications from a single field station, assuming tha.t such a. field'station is i:he only one having new indications to transmit at the beginnlng cf the cycle.

Automatic start.--Reierxing to Fig. 2B, a change in condition o! the detector track section or a, change in condition of the traflic coutrolling devices at the station mayoccur for efiecting the initiatldn of the system for the transmission of indieations. Although the detailed circuits a.re not shown it will be assumed (and readiiy understood by referring to Fig. 2 of Patent N0. 2049,406) that any such change may so condition the circults that relay CH is dropped. The dr0pping of relay CH closes a. circuit for picking up relay SI whlch extends from back contact l80 of reia.y CHR back contact I8! of relay 83 and upper winding of relay SI to II: will be vassumed. at present (anti later explained) that, relay S1 remains picked up throughout the following indication cycle. The closure of front contact 182 015 relay SI starts the Operation of the oscillator mixer tube OSM by completlng the plate circuii; of thls tube.

Tube OSM is a muiti-electrode tube known in the radio art as a, Pentagrid converter. Such a. tube is shown und its operation is described 011 page 23 of the R. C. A. Cunningham Radiotron Manual Technical Series RC-12, copyright 1934. This tube comprises hea.ter l9li, ca.thode l9i, grids l92, l93, I94 und l95 and piate I9G. Althoush no connection is shown to heater l90, it will be understood that thig element may be energized from any proper source of heater current supply In this tube, cathode Nil and the flrst two grids 192 and I83 may be regarded a.s a comp'ositga cathode which suppiies n modflaiaed eleqtron stream. The modulated eiectron stream has its frequency determined by the cha.xwteristlcs of the osciliating circult including transformer OST. condensex 080 und inductance Oh. 'Ihe modulated electron streamis further Controlled by the other gxids IN ax 1d II! und plate II. In other w0rds srid III is th e control grid i'or the oscillator portion o! the taube. grld III is the anode for the oscillator and grids I (connected together within the taube) are used to accelerate the electron st reain from the cathode. whlch acceiera.tion is controlled o: modulated by Irequency P app lied to grid IM by way oi transtormer I'IF.

Grids I9! eie ctpicailv shield the signal control grid I from the oti n'ar electrodes, which increases the output impedance oi' i:he taube to provide a desirxble characteristic ga.in. Fron: the above brief expianatlon lt will be understood that the osi:illator grid circuit, including grid l92, is macle to oscillaige at'frequ6ncy I so thai'. the electron stream in flowing through g'rid l92is moduiated a.t this frequencs. This modulated electrbn stream comes under the infiuence of grld I95 which is dperated ab a positive potential with respect to the cathode and as a resuii; the electron stream is accelerated towa.rd platze l86 by grid I95. The incoming monii;oring frequency f applied to grid l9, preferably monitors or dominates the eiectron stream (aiready modulated at the oscillator frequency) thus producing platz: current,- the frequenc'y '0f which ha.s a definite relation to the synclnonizing er monitorlng frequency f. Since transformer 4'IFI applies the oscillator Irequency f! und the indication slgna.l irequency f, both o1 which ha.ve practicaily the same number of cycles per unit cf time, from the platze circuit i;o the line circult by way o1 the composite set a.t the transmitting field station, these i;wo irequencies will be received in the control omce.

However, the controi ofice apparatus has noi; yet been started into operation so that frequency 1 is not yet appiied to the iine circuit. Frequency f is received in the control oillce and Dassed through tr'ansiormer GTF'R, ievel control 6LC, transiormer G'I'F'Rl', amplifl er 4AI, transformer 4'I'FR2, amplifler 4A2, transformer 4'I'FR3 und. rectifier IRC thifough the lower winding of relay MB. lt will beunderstood tha.t the above described units in the coutrol opflce are designed to eifectively pass frequency f as weil as frequency f, which frequenciesas ab0ve mentionecl. are practically the saure.

Relay MB is therefore picked up and a circuit is closed for picking up relay CF which extendls from from; contaci; 51 of relay MB, couduc'tor l2l, back contact 65 01 relay SC anti winding of relay CF ivo Relay CF closes a circuit a1; its freut contact B8 for picking up relay0C a.nd relay 0C closes a circuii; for picking up relay 2F which extends from back coutact 25 of relay E, front contact 25 of relay OC, back contact 6 of reiay C, traut contaci; 20 of ;relay CF concluctor l22, back contaci; I9 oi relay LS and upper winding of relay 2F to The picking up of relay 2F applies frequency f the llne circuit as soon as relay CF picks up to starb the generators into operation.

The system now operates through a cycle as line durlug the on perieds because lt !s assumed that relay C ls dewn and its back centact 26 ls clesed. A stlck circult ls cl0sed for relay CF, when relay SA picks up, whlch extends from freut centact I2 of relay SA, ceuducter l24, freut contact 10 and wiuding 01 relay CF te As seen as the ofllce appl1es frequeucy f to the line clrcuit it menlters er demlnates the frequeucy 'f which 1s applled te the liue circu1t at the trausmittiug stati0n. te preduce frequency f preferably haviug a definite frequency relatien te frequency f. It will therefere ba understeed that'durlng the follewing cycIe ef eperatleus, frequeucy f 1s selectively applled to the liue 1er transmitting indicatiens. Frequency f is applied when the statlou start is initlated, from the' secoudary ef transfermer 4'IF'I, by way ef back centact I83 ofrelay SB and freut centact 104 of relay SI Durlng the fellewlng cycle. frequency 1 is received threugh level contrel netwerk 3LC and transformer 3'I'F and ampllfied by amplifler 3A from which lt 1s applied te osclllater mixer grld I94 by way ef transfermer 3'I'F.

Dur-Ing the fellowing cycle, relay SB will be picked up and siuce frentcentacts I83 and l84 are closed, indicatien codes are transmitted in accerdance with the eperatiens of relays FB PF and PB as will now be described. During the ceuditioning on period, the epening of back ceutact I83 ef relay SB removes frequency f from the line, siuce neither freut centact I85 ef relay FF nor 186 of relay PB is closed. Relay MB in the offlce is dropped during the first eff period when freut centact 9l ef relay FB and back centact 10 of relay E are both open.

Registratz'on of a fleld station.Te avoid coufuslou regarding the perieds ef selectien, transmisslon and executien ef indicatiens, thz erder ef eccurrence ef these perleds will be briefly poluted eut befere the mauner ef transmittiug indicatiens is explalned in detall. The flrst eff" indicatieu is selected at the station during the first oft period and ls executed in the. efflce during the first on period. The first on indiatien is selected at the statien during the first off period, is transmltted and received duriug the first on period and 1s executed in the office during the second eff period. The second oflz indication is selected at the statten durlug the f1rst o period, is transmltted and received during the second elf period and is executed in the eflice duriug the second on period. The second on iudicatleu is selected at the statieu duriug the second oft period, is transmitted and received duriug the second on period and is executed in the oflice during the third eff peried. The th1rd 01T indicatien is selected at the statien during the second on period, is transmitted and recelved during the thlrd oft period and is executed in the eflice during the third en period. The third on indicatien 1s selected at the station during the third ofi period, istransmitted and received duriug the third on period and 1s executed in the oifice during the clearing eut period.-

At the particJular statten havi ug indicatiens to trausmit, relay SI is up and by meaus ef 1ts freut ceutact I 81 the indicatien cede transmitting relays PB and PF are reudered effective. It will be assumed that the transmitting statien, illustrated in Figs. 2A and 2B, identifies itself in the control eflice by a. cede cemprislng a.n impulse of lndlcatieu carriefcurrentfl daring the:flrst e and thaflrst on peri0ds'as determiued by jumpers l08 and l89 in thei't full line peslttious. This code comblnatieu poSitieu's the polar centacts'ef pllot relays IPT and 2PT (see Fig. 1C) te the1r rlght hand positieus for selecting statlen relay ST, which ls the relay fer identlfying the lllustrated statlen in the coutrel offlce. Y

When relay FB 1s plcked up during thc. ceudltloning on period, the flrst efi" lndlcatiou ls selected. Relay PB ls plcked up over a clrcu1t exteuding from jumper I in its full line pesitien, back contacts 200, 20I and 202 ef relays IVR 2V and 3V respectlvely, freut ceutact I9'l of relay FB winding ef relay PB and frentcoutact I8! ef relay SI to 'I'hls indlcaJtlen is transmitted over the Ihre clrcuit during the first elf period when relay F13 dreps, at which time a stick circuit 1s completed for relay PB exteud- Ing from freut c0ntact 198 of relay PB, back centact l9'l ef relay FB winding of relay PB and freut centact 181 of relay SI to Relay PB up determines that indic'atieu frequeucy f shall be transmltted over the llne circuit during the first off period. The circuit for transmitting this indicatien carrier current may be traced from the right hand termiual ef the secendary winding ef transfermer 4TF'I, freut centact l84 of relay SI freut centact l83 ef relay SB back centact 203-0f relay FB freut ceutact I86 ef relay PB cenducter 204 te the upper line cenducter by way of the compesi te set, from the upper 1iue couductor in the effice by way ef the cempesite set, conducters H2 and II, coudenser- 4C, pr'mary win dfng ef transfermer 4'I'FR, conductors 12 and H3 to the lower line by way ef the cempeslte sei; in the eflce, from the lower line cenducter by way ef the cempes1te set at the statien and conducter 205 te theleft hand terminal ef trausformer TF'I,

The transmlssien ef th1s first oft iudicatien cede is terminated when rclay FB picks up and epens the abeve descrlbed circuit at back centact 203. When relay F13picks up te terminate this first efi cede the abeve descrlbed stlck circuit fer relay PB is epeued at back coutact I9! and relay PB 1s dropped. In the event that jumper I88 is in its alternate dotted line pesition, then relay PB will net be picked up so tha-t ne indicatien carrier curreut will be transmitted duriug the flrst efi' period.

The first on lndication code is selected when relay F'B is drepped during the t1rst elf period. A circuit is clesed for picking up relay PF which extends from jumper 189 in its full line pesit1'en, back contact 206 efrelay 2V, freut coutact 201 of relay VP back centact 208 of relay FB winding ef relay PF and freut centact I8! ef relay SI te When relay FB is picked up during the first on period a. stick circuit is clesed fer relay PF which extends from freut ceutact 209 ef relay PF freut ceutact 208 ef relay FB winding ef relay PF and freut coutact I8! ef rela.y SI te Thi s stick clrcuit is brekeu and relay PF 1s drepped during the s'econd efi" period, when relay FB drops and epens the abeve described stick circuit at freut centact 208.

Carrier current frequency f is transmitted during the first on period (while relay FB is picked up) over t-he abeve described circuit, but which now extends threugh freut ceutact I83 ef relay SE freut centact 203 ef relay IF'B and freut contact I of relay FF. Ihis carrier cur- 75 rent Impulse ls terminated when relay l-"B drops durlng the second "cf!" perlod and opens the above described clrcult als front contact 203. In the event that Jumper II! ls in 1ts alternate dotted line poslttion, then relay PF will nol; be

plcked up und no carrler current frequency will be transmltted over the llne clrcult durlng the flrst .on perlod.

Referring to the control ofllce, the lndlcatlon trequency f received durlng the flrst ofl"period ls applled to the lnput 01 ampllfier AI .by way of level conttol network ILC and ls ampllfied by ampllfler s IA I and IA2 w1th rectlfled (nirrent resultlng from t.hls carrler frequency being effectlve to plck up relay MB over a. clrcuit which maybe traced from the upper l ;ermlnal cf the secondary wlndlngs of transformer ITFR3, couductot I25, rectlfler 4RC. front ccntacts 11 anal 16 of relays CF and SC respectlvely. conductor cuit for relay MB is through contacts l! and 16 instead of through back contact 8'l.

The first ofi indicatiori code is executed in the control fllce when relay FA drops als the beglnning 01 the first "on perlod by closlng a circuit which extends from (B+), freut contact 8I of relay MB, back contact 82 -of r'elay FA,

conductor l28, front contact 83 cf re1ay CF, back contacts 86 and 85 of re1ays 3V and 2V respectively, front contact 86 of relay W, conductor I29, and wlnding of relay IPT to (CN). The polar contacts of relay IPT a.re posltioned to the right in response to the closure of this executing circuit. The executlon of the flrst oft code is terminated when relay FA 1s picked up at the beginnlng of the second o perlod, by the openlng of back contact 82.

The first on code received in the control ofiice during the first on perlod 1s eflective to pick up relay MF over a clrcuit which may be traced from the upper secondary winding of transformer 4TFR3, conductor I25, rectifier 4RC, front; contacts 'l'l am]. 16 of relays CF and SO respectively, conductor 126, front contact 15 cf relay FB, either front contact 88 of relay ZF or front contact 89 of relay IF (whlchever ls up) and lower wind.ing of relay MF to the lower terminal of the secondary winding o& transformer ATFR3. Relay 1VIF 1s stuck up throughout the second off period by means of a first stick circuit which is closed when rela.y E picks up and which extends from freut contact 18 of relay SB, front contact 19 of relay E, conductor ginning of the second ofif I30, front contact 90, and. upper winding of relay MIE to Before relay E drops during the second off period a. second stlck circult is closed for relay M'Fwhich extends from front contact 18 of relay SB, concluctor l3l, back contact 9l of relay FIB, front ctmtact 90 and upper winding of relay NIE to The executing circuit for the flrst "on" code is completed when relay FA picks up als the' beperiod and. extends from (B+) front contact 92 of relay MB, front contact 93 of relay FA, conductor l32, front Cont act 9l oi relay VP back contact !I6of relay 2V, conductor I3I. and wlndlng of relay 2PT to (CN). Thls reults in posltlonlng the polar contacts of relay -21"T to the rlght. The execution cf the flrst"on" lndlcatlon code ls terminated when relay FA 1s dropped at the beglnning of the second "on perlod and (mens lts .front contact 93. When relay IV ls plcked up durlng the second "oft" perlod relay ST-ls plcked up over a circuit extendlng from front contact 98 cf relay IV, conductdr l, polar contacts 99 and l of relays IP'I and IFT in thelr rlght band positions and wlnding of relay ST to It will be obvlous that other transmltting statlons will positlon pilot relays IPT and 2PT in other combinatlons of posltions for identifying these other stations in a manner which will be obvlous from the above example, considerlng that a fleld statlonmay apply a pulse (lmpulse cf ca.rri er frequency f) or a nun-pulse (no impulse of carrier frequen cy f) during the oft and on perlods cf the statlon selecting steps of the cycle. It will be understood that additional steps cf the cycle may be allotbed for transmittlng similar codes In systems of larger slze the number of codes provlded .belng equal to four for one step (an ofiand an perlod) slxteen for two steps, sixty-four for three steps, etc.

Transmission o! indicatitms.-After thus having registered or ldentifled the transmitting field station in the contro1 oflce* the remaihlng steps of the cycle are employed for the transmissio-n of* indlcations from the registered station. For

the,purpose of lllustratlng lndication transmiss1on trackrelay T and signal repeating relay M are lllustrated in Flg. 2B. I1: is assumed that both of these relays are energized to repeat the condition t ha.t the 'assoclated track section is unoccupled and that all slgnals associated there- .wlth are ab stop.

The second off lndlcatlon is selected durlng the firsl; on perlod when relay FB picks up and with relay T 'picked up, relay PB 1s dropped. This results in a, nun-pulse for the second off indication so that relay MB will be dro-pped during the second oft period, when relay FB drops and opens lts freut ccntact 9I. 'I'his is because at this ti1'fie relay E will be up with its back contact. 19 open so that the stick circuit for rela.y MB will be deenergized anti, since no indlcation pulse is received, relay MB ls dropped.

The second ofi lndicatlon is executed during l;he second on perlod whe'n relay FA drops for closing a clrcuit which extends from (B), back contact 6I cf relay MB, back contact 82 of relay FA, conductor I28, front contact 83 of relay CF, back contact 8 of relay 3V, front con tact 85 of relay 2V, conductor I35, front contact llll of relay ST a.nd wlnding of relay IIR to (CN). Current fiowing in this direction over this circuit positions the polar contacts of relay IIR to the left for closing an lndication circuit in the control oflce (not shown) which indicates thal; relay T at the field station is picked up. The second 01T execution period is terminatetl ab the beginning cf the thlxd o period, when relay FA picks up and opens the aboVe described clrcuit ab back contact 82.

um m of relay m3 winding'of telay m3 and front contact 181 cf relay S1 tc(). Flom the abve example lt will be-understood that relay PB is stuck up (when picked up duringthe first on" period) throughout i:he second "cf!" period in a manner which will be obvious from the above explanation relating to the sticking cf relay PB throughout the first "et!" period. With a pulse received in the contrcl ofllce during .the

second "elf" period, relay MB will be energized over the previously described circuit and the executing circuit Will extend from (B+) at freut 20 period, but ii: will merely'be mentioned that a pulse is transmitted dliring the second on period i! relay M is down for picking up relay P1 over a circuit including back contact 2II cf relay-M front'contact 2I2 cf relay lV back contact 2 I3 of 5 relay 3V back contact 201 cf relay VP back coutact' 208 of rela3rv FB winding of relay PI! and freut contact l81 of telay SI to With relay FF; picked up the second on code is a pulse for picking up relay M1 in the con'trol cflice, which 30 will be stuck upthroughout the third -o period.

The executing circuit for the secondon" pulse' code will be completed while. relay FA is picked up, which is eifective to position the polar cantacts cf relay 2IR 'to the right by way cf a circuit extending thrcugh front contact III2 of relay ST. Obviously if relay M! is up, then a non-pulse for the second on code is transmltted and relay MF will be down, when the execution o1 the second on code takes place, for applying (B) over the above described circuit to relay 2IR.

It will be obvious from the aboveexamples that a choice of four indicatlons from the transmitting field stationis provided toindicate any one cf four conditions at euch step- ("ofi and on p'eriod) of the cycle. It will furthermore be obvious tha1; freut contacts cf stepping relays 2V and 3V may connect to additional selecting circuits for applying additional indication codes from the transmitting field station.

Lock-out between stations. lt may happen that changes occur a1: a pluxality of fleld stations at the saxne tixne, cr in rapid succession, so that more than one station will have new indications to transmii; a1; the beginning cf a cycle. In order to prevent more than one station remaining in ac-. tive associa;tion with the line after the station selection steps cf a cycle, lock out means are provided at ea.ch station which are etfective to give preference to that station having a superior code and to rule 01T or lock out another statlon or sta-' tions (having inferior c pdes) having indications 1:0 transmit during this cycle.

It will be assumed that changes occur at substantially the same time at the flrst field station illustrated in Figs. 2A and 23 and at the second field station from the control oflice; In this event relay CH will be dropped and a. sim ilar change relay a1: the second station will be down at the same time. The dropping cf relay CI-I picks up relay S1 as previously described and a. similar cir-' cuii: is completed at the second station for picking up its SI relay.

Ii: will be recalled that the illustrated (flrst) y staticn registered itselt in the ofiice by transmit ting code pulse, pulse during the first o and pulse" code.

the flrst "an" periods. The second statin will have another code such as pulse. hon-pulse. A pulse is superior to a. non-pulse. 'Since all the station; are connecii6d to the line and receive the indication carrier 'frequency f, the associated ME relays will-pick up in response to a pulse" code and 1emain down in r"esponse to a. non- The flrst "ofl!" code transmitted by both the flrsb and second stations is pulse. Therefore the SI relays at both stations will remain up in response to this code. dueto -t;he code selecting circuits. Relay 81 is held up by means.of its pick-upcircuit until relay SB picks up durin the co1iditicning on" period to open this pick-up ci rcuit at back contact III. Before relay SB picks up, relay SIS is picked up (during the conditicning on periodl over a circuit extending from front contacts2ll and 215 of relays 1".B and SI and winding cf relay SIS to A stick circuit is closed for relay S1 which extends from back contacts 22l and 222 of relays PF and ME respectivelyront contact 2l8 of relay FB, tront contact 2I9 and lower winding of relay SI v to .With relay SA picked up this stick circuit extends from front contact 223 of relay SA, freut contact 220 of relay SISR' freut contact 2l9 and lower winding cf relay SI to This stick circuit is opened by relay SIS dropping in the flrst off" period because cf open front contaci: 2M of relay FB The above discussion also applies to the manner in which the SI relay at the second station is maintained picked up anti! the associated FB relay drops in the flrst oif" period.

When relay NIE picks up at the flrst and second statians in response to the flrst oft code "pulse" (puise because the PB relays a.t both stations.are up), the selecting stick circuits for the SE relays at these stations are completed for maintaining them enel3i2ed. This circuit for relay SI extends from Iront contacts 2l6 and 2l'l cf relays PB and ME respectively, back contact 2I8 of relay FB, front contact 2l9 and lower winding of rlay SI to A similar circuii. is completed at the second station.

With the SI relays up. the associated SIS relays pick up when the associated FB relays pick up and close their front contacts (such as oonta.ct 2M in F'ig. 2B) in the flr st on period. With relay SIS up, relay SI is Stuck up over the prevlously described circuit including front contact 220 until relay SIS drops in the second ofi' period. Before f;he dropping cf relay SIS relay 2V picks up and completes the permanent stick circuit for relay SI whicl:i extends from front contact 223 of relay SA front; contact 224 cf relay 2V, front contact 2l9 and lower winding 01' relay S1 to Relay SI is not dropped when the first on code selection is made because relay ME is up and relay PF is up to complete the selecting stick clrcuit for relay SI which extends from front contacts 22I and 222 of relays PF and ME respectively, freut contact 218 of relay FB front contact 2l9 and lower winding of relay S1 t0 Relay PF is up because the first station transmits a pulse code for the first on and relay ME is up because lt registers the reception of the pulse first "0n code.

IheSI relay at the second station is dropped in response to a pulse becausc the ME and PF relays are out cf correspondence at that station so that the selecting stick circuit cannot be com'pleted. This is befor the first on code t:ause the ME relay at the second statlon=plcks up to registr the reception of the pulse" cqde, but the PF relay at the second statlon 1s down because this statlon transmltsa. non-pulse" for the flrst "an" ende. With the SI' relay down at the seoond statlon. lt cannot be agaln plcked up durlng this cycle because 01 an open back contact similar to l8l cf relay SB. thus rule d ofl or locked out and is prevented fr0m transmitting 1ts lndicatlons because cf open front cont act slmilar to IB'I of relay SIR Relay 81 at the flrst station however remains up and its lxidlcatlons are transmltted.

In the above example only-two statlons are consldered as being ready 1:0 send ln indications and one cf these statlonswas dropped out durlng the first on" code. 'I'he same plan of operation occurs lrrespective of the number 01 statlons ready a1; the same tlme to send in indlcatlons. such statlons being dropped out one or more at a tlme during each code transmission, untll only one station is left wlth its SI relay energized. after the full number cf station selecting steps has been taken.

This scheme cf station selectlon for lncomlng lndications ls or 1. the basls of superlority o1 code calls. From the example above given, lt will be seen that a statlon having a code', call with a pulse" for t he first code will drop out all other statio'ns' having a. ende call with -a non-pulse" for th flrst ende. Thls is because the flrst (superlor) of these statlons has its code transmlttlng relay and its code recelvlng 'relay in correspondlng positions, whlle the ende transmlttlng relays and the code recelvlng relays at the other stations are in non-correspondlng positlons, so that the SI relays at these other stations have no selectlng stlck circults completcd and consequently they are dropped out.

Although not lllustrated -ln the dra.wlngs lt will be undersbood that the CH relay at the superior station,whlch ls eifective to transmlt its indlcatlons during a cycle, ls plcked up o1 resensitlzed after the station selectlng codes have been transmltted, as illustrated in Flg. 2 of Patent N0. 2,049,406. At those stations whlch are ruled ofl,

the CH relays remaln down so that the assoclated SI relays are again picked up at the beginning of the next operating cycle and the most superlor statlon of those still having lndicatlons to transmit registers ltself in the control oflilce in the 'manner prevlously descrlbed, whlle the others take thelr turn in reglsterlng themselves in the control oflce in accordance wlth the superiorlty of thelr ende calls.

Duplex opefat i0n.-It has been pointed out that control and lndieatlon cycles may occur separately or slmultaneously. The operations for separate control and lndicatlon cycles have been descrlbed and lt will now be pointed out how tl1e system functions when controls and Indicatlons are transmltted durlng the same cycle. An actuatlon of the starting button in the offlce results in plcklng up of the assoclated CD relay. Thls relay may be plcked up ab the beglnnlng of a cycle any time up to the end cf the perlod marked oft by the picklng up o! relay SA ancl the consequent openlng of it's back contact I2. If a fleld statlonhas initia.ted thesystemwhich results in the plcking up o1. relay CF in the control offlce as previously described, thls relay CF may be picked up over the previously described clrcuit a.ny time up to the perlod marked oft by the picking up cf relay SC and the consequent openlng of it-s back contact 85. When relay CF 1s picked up it is 'I'he second statlon ls stuck up over the preflously lescribed dr cult extendlng through front contact I2 of relay SA and when telay CD ls plcked up lt is Stuck up over the prevlously descrlbed clrcult including back contact 62 of relay 3V.

Wlth relays CD and CF picked up due to ofllce and field Starts the system runs through a cycle of operatlons as before, but s lnce bak contact 19 of relay LS is open and front contacts 1,8, etc. 01 relay CD are closed the carrler frequency f is not lnvaxizibly applied to the line circult by relay 2F remaining up, as Was the case durlng the transmlsslon' of lndlcatlons alone Dill; ca.rrler frequencles f f* are selectlvely applled in accbrdance wlth the code jumper and control lever connectlons.

'Ihe stepping- 9.nd lmpulsing operations will be efiected as previously descrlbed; with the station being selected for controls 537 the selective energlzatlon of the associated SO relay in a manner whlch has already been explained. Since the SI relay at the statlon having lndications to transmit is also picked up, the associa.ted PB and PF relays will be selectively actuated to apply the indlcation ende, thlsbecause of closed front contaet such as I8! of relay SI.

The resulting cycle 013 operations ls thus the same, in so far as thetransmlsslon of control codes (made up 0f frequencies f and/or F) over the llne circult is concerned, as was previously described in connectlon wlth a control cycle alone. Slmilarly the resulting o'perations duringthe cycle,*lnsofar as transmltting the indlcation carrler fre'quency f over the lln'e circuit during the "ofi and an perlods ls coucerned, is the same as described for a, cycle during which indications alone were transmltted. It ls believed that the above brief explanation is sufllclent to indicate that, slnce the transmission cf controls and the transmission of lndications are efiected by the separate and distlnct conditioning 01 the line circult, these tra'nsmissions may be combined and brought aboul; -during a Single cycle of operations in the manner prevlously pointed out.

Synchrcmi2ing carri@r frequency f.-The above explanatlon polnted out that the Indication ende transmltting frequency f is obtalned from the oscillator mlxer taube at the transmit tmg station by modulating the oscillator frecoming synchronizlng frequency f generated in t-he control office with a. force to cause the fre-' quency 7 to follow the frequency ;f so as 120 have a definite frequency relation thereto. 'I'he purpose 01 making frequency f definltely relative to trequ ncy f ls 1:0 prevent interference and possible neutrallzatlon of the I frequencies when superimposed on the line circult; at two or more trans mlttlng stations. If frequency f were to be generated locally at each station or Ware to follow frequency f rather than frequency f then when two or more stations picked up their SI relays in an attempt to transmit indications durlng the same cycle, it will be obvious that; the phase angle between two or more df these frequenclesapplied to the line might be such tha.t they would cancel each other a.nd not be received in the control ofllce and at the transmittlng stations. By dominaLting the local oscillator frequencies f generated at each transmitting station, by a common fixed synchronizing frequency f generated in thecontrol ofi1ce, it will be apparent that the resultant indlcation code transmitting frequencies f applied 130 the lin e at 

